ext4: fix use-after-free race with debug_want_extra_isize

commit 7bc04c5c2cc467c5b40f2b03ba08da174a0d5fa7 upstream.

When remounting with debug_want_extra_isize, we were not performing the
same checks that we do during a normal mount.  That allowed us to set a
value for s_want_extra_isize that reached outside the s_inode_size.

Fixes: e2b911c53584 ("ext4: clean up feature test macros with predicate functions")
Reported-by: syzbot+f584efa0ac7213c226b7@syzkaller.appspotmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 4.9: The debug_want_extra_isize mount option is not
 supported]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 3261478bfc32dd31454da6c91de5db89a44beb6a..cea813adbe12fa815a2d04309e44c740f7e70b0f 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3342,6 +3342,36 @@ int ext4_calculate_overhead(struct super_block *sb)
        return 0;
 }
 
+static void ext4_clamp_want_extra_isize(struct super_block *sb)
+{
+       struct ext4_sb_info *sbi = EXT4_SB(sb);
+       struct ext4_super_block *es = sbi->s_es;
+
+       /* determine the minimum size of new large inodes, if present */
+       if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
+               sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
+                                                    EXT4_GOOD_OLD_INODE_SIZE;
+               if (ext4_has_feature_extra_isize(sb)) {
+                       if (sbi->s_want_extra_isize <
+                           le16_to_cpu(es->s_want_extra_isize))
+                               sbi->s_want_extra_isize =
+                                       le16_to_cpu(es->s_want_extra_isize);
+                       if (sbi->s_want_extra_isize <
+                           le16_to_cpu(es->s_min_extra_isize))
+                               sbi->s_want_extra_isize =
+                                       le16_to_cpu(es->s_min_extra_isize);
+               }
+       }
+       /* Check if enough inode space is available */
+       if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
+                                                       sbi->s_inode_size) {
+               sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
+                                                      EXT4_GOOD_OLD_INODE_SIZE;
+               ext4_msg(sb, KERN_INFO,
+                        "required extra inode space not available");
+       }
+}
+
 static void ext4_set_resv_clusters(struct super_block *sb)
 {
        ext4_fsblk_t resv_clusters;
@@ -4156,29 +4186,7 @@ no_journal:
        if (ext4_setup_super(sb, es, sb->s_flags & MS_RDONLY))
                sb->s_flags |= MS_RDONLY;
 
-       /* determine the minimum size of new large inodes, if present */
-       if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
-               sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
-                                                    EXT4_GOOD_OLD_INODE_SIZE;
-               if (ext4_has_feature_extra_isize(sb)) {
-                       if (sbi->s_want_extra_isize <
-                           le16_to_cpu(es->s_want_extra_isize))
-                               sbi->s_want_extra_isize =
-                                       le16_to_cpu(es->s_want_extra_isize);
-                       if (sbi->s_want_extra_isize <
-                           le16_to_cpu(es->s_min_extra_isize))
-                               sbi->s_want_extra_isize =
-                                       le16_to_cpu(es->s_min_extra_isize);
-               }
-       }
-       /* Check if enough inode space is available */
-       if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
-                                                       sbi->s_inode_size) {
-               sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
-                                                      EXT4_GOOD_OLD_INODE_SIZE;
-               ext4_msg(sb, KERN_INFO, "required extra inode space not"
-                        "available");
-       }
+       ext4_clamp_want_extra_isize(sb);
 
        ext4_set_resv_clusters(sb);
 
@@ -4959,6 +4967,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
                goto restore_opts;
        }
 
+       ext4_clamp_want_extra_isize(sb);
+
        if ((old_opts.s_mount_opt & EXT4_MOUNT_JOURNAL_CHECKSUM) ^
            test_opt(sb, JOURNAL_CHECKSUM)) {
                ext4_msg(sb, KERN_ERR, "changing journal_checksum "